'\" t
.TH "SD_BUS_WAIT" "3" "" "systemd 257" "sd_bus_wait"
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.SH "NAME"
sd_bus_wait \- Wait for I/O on a bus connection
.SH "SYNOPSIS"
.sp
.ft B
.nf
#include <systemd/sd\-bus\&.h>
.fi
.ft
.HP \w'int\ sd_bus_wait('u
.BI "int sd_bus_wait(sd_bus\ *" "bus" ", uint64_t\ " "timeout_usec" ");"
.SH "DESCRIPTION"
.PP
\fBsd_bus_wait()\fR
synchronously waits for I/O on the specified bus connection object\&. This function is supposed to be called whenever
\fBsd_bus_process\fR(3)
returns zero, indicating that no work is pending on the connection\&. Internally, this call invokes
\fBppoll\fR(2), to wait for I/O on the bus connection\&. If the
\fItimeout_usec\fR
parameter is specified, the call will block at most for the specified amount of time in μs\&. Pass
\fBUINT64_MAX\fR
to permit it to sleep indefinitely\&.
.PP
After each invocation of
\fBsd_bus_wait()\fR
the
\fBsd_bus_process()\fR
call should be invoked in order to process any now pending I/O work\&.
.PP
Note that
\fBsd_bus_wait()\fR
is suitable only for simple programs as it does not permit waiting for other I/O events\&. For more complex programs either connect the bus connection object to an external event loop using
\fBsd_bus_get_fd\fR(3)
or to an
\fBsd-event\fR(3)
event loop using
\fBsd_bus_attach_event\fR(3)\&.
.SH "RETURN VALUE"
.PP
If any I/O was seen, a positive value is returned, zero otherwise\&. If an error occurs, a negative
\fIerrno\fR\-style error code is returned\&.
.SS "Errors"
.PP
Returned errors may indicate the following problems:
.PP
\fB\-EINVAL\fR
.RS 4
An invalid bus object was passed\&.
.RE
.PP
\fB\-ECHILD\fR
.RS 4
The bus connection was allocated in a parent process and is being reused in a child process after
\fBfork()\fR\&.
.RE
.PP
\fB\-ENOTCONN\fR
.RS 4
The bus connection has been terminated already\&.
.RE
.SH "NOTES"
.PP
Functions described here are available as a shared library, which can be compiled against and linked to with the
\fBlibsystemd\fR\ \&\fBpkg-config\fR(1)
file\&.
.PP
The code described here uses
\fBgetenv\fR(3), which is declared to be not multi\-thread\-safe\&. This means that the code calling the functions described here must not call
\fBsetenv\fR(3)
from a parallel thread\&. It is recommended to only do calls to
\fBsetenv()\fR
from an early phase of the program when no other threads have been started\&.
.SH "HISTORY"
.PP
\fBsd_bus_wait()\fR
was added in version 240\&.
.SH "SEE ALSO"
.PP
\fBsystemd\fR(1), \fBsd-bus\fR(3), \fBsd_bus_process\fR(3), \fBsd_bus_get_fd\fR(3), \fBsd-event\fR(3), \fBsd_bus_attach_event\fR(3)
